August 5, 2009: This ‘before’ picture shows the disintegrating ice shelf before it floated away. CREDIT: Jason Box, Byrd Polar Research Center, Ohio State University.

An ice shelf is poised to break off from a Greenland glacier and float out to sea as an island twice the size of Manhattan, scientists say.

“I don’t know exactly when,” Jason Box, a climatologist with Ohio State Unversity’s Byrd Polar Research Center, told OurAmazingPlanet. “I wouldn’t be surprised if it happened today — or if it happened next summer.”

Just a year ago, in August 2010, the same glacier produced an even larger iceberg — a mass of ice four times the size of Manhattan, the largest in recorded Greenland history — yet researchers warn that the next spectacular break could have more-dire consequences.

Box said it’s not clear when the 62-square-mile (160 square kilometers) ice shelf, which is dangling from Greenland’s Petermann Glacier, will detach from the mainland. “I think it’s more likely to occur during periods of melt, and that’s coming to an end, so I’m losing confidence it’s going to break this year,” Box said.

Ice shelves are enormous plates of ice that float on polar seas but are connected to the shoreline by the land-bound glaciers that feed into them.

During much of the Arctic melt season, summer sunlight pounds the Earth’s highest latitudes nearly 24 hours a day. Melting typically draws to a close in early to mid-September, when cooler temperatures and shorter days arrive.

Box said scientists first noticed a jagged crack in the glacier’s ice — a growing rift he dubbed ‘The Big Kahuna’ — in 2008. However, a subsequent search through satellite data revealed the rift first appeared about eight years earlier.

“We can see the crack widening in the past year through satellite pictures, so it seems imminent,” Box said.

Ice shelf collapse can affect sea levels.

to read more, go to:   http://www.livescience.com/15890-greenland-ice-chunk-break.html